python: Sort migrations/management command imports with isort.

This is a preparatory commit for using isort for sorting all of our
imports, merging changes to files where we can easily review the
changes as something we're happy with.

These are also files with relatively little active development, which
means we don't expect much merge conflict risk from these changes.

analytics/management/commands/clear_single_stat.py

@@ -5,6 +5,7 @@ from django.core.management.base import BaseCommand, CommandError
 
 from analytics.lib.counts import COUNT_STATS, do_drop_single_stat
 
+
 class Command(BaseCommand):
     help = """Clear analytics tables."""